1. Field of the Invention
This invention relates to the recovery of anhydrous chloral from a mixture containing chloral and water and/or chloral hydrate and other components. More particularly, it relates to a process for extracting 99.9% or more of the water from the chloral/water mixture by azeotropic distillation at atmospheric pressure using ethylene dichloride as an azeotroping agent and one or more distillation columns.
2. Description of Related Art
Over the years, there have been several methods employed to remove trichloroacetaldehyde (hereafter, "chloral") from aqueous solutions in which it is present. Where the separated chloral is to be used, for example, in other chemicals, it may be of critical importance that the chloral be as free of water as possible. In this context, the presence of even relatively minute quantities of water can have a substantially adverse effect on the performance of the end chloral product.
One of the more common approaches to the dehydration of chloral has been the use of azeotropic distillation. This processes involves contacting the chloral-containing solution with a dehydrating agent under conditions sufficient to form an azeotropic mixture. Examples of dehydrating agents which have been used in this process include benzene or n-hexane (see, e.g., U.S. Pat. No. 2,584,036), or hydrochloric acid (see, e.g., U.S. Pat. No. 2,746,912). Other process for the removal of water from chloral are known, for example, distillation from sulfuric acid (see, e.g., U.S. Pat. No. 4,513,152 and the patent references cited therein). However, all these processes produce chloral which is contaminated with solvent and/or contains a quantity of water which is unacceptable for many uses or have large waste streams associated with their practice.
Currently, as shown in U.S. Pat. Nos. 4,814,528 and 4,628,122, the aqueous by-product from the manufacture of vinyl chloride, ethylene dichloride, or in general, the oxychlorination of ethylene, must be incinerated or neutralized and destroyed prior to discharge or disposal.
One attempt to obtain dry chloral using ethylene dichloride or 1,2-dichloroethane (hereafter, "EDC") in an azeotropic distillation process is described by Schussler, et al, in U.S. Pat. No. 4,814,528. In the process described, EDC, the contained impurity, chloral and water are subjected to azeotropic distillation wherein EDC is used as the azeotropic agent resulting in a dried EDC containing chloral. At atmospheric pressure this process was described as only reducing the water content to between 1% and 3% by weight (relative to chloral content).
The percentage of water in the end product of the Schussler, et al. process was greatly decreased by application of superatmospheric pressure to the azeotropic mixture during distillation. Although more effective than prior art azeotropic distillations of chloral at atmospheric pressure, the Schussler, et al., approach requires use of specialized distillation equipment. As a result, this process suffers from increased manufacturing cost as well as operating risks associated with the use of pressurized liquids and gases. Further, this method would require processing extremely large volumes of EDC for relatively small amounts of isolated chloral. For example, the EDC to chloral ratio used for the work described in Schussler, et al., is between 94:1 and 171:1.
Using the same dehydrating agent (EDC), researchers at the Institute for Organic Industry in Warsaw and the Polytechnical University of Szozecin in Poland reported that they obtained 98.5-98.9% anhydrous chloral in an azeotropic distillation (see, Polish Patent No. 102,372 to Cieslak, et al., and Cieslak, et al., Przem. Chem 56 (11) 594-598 (1977)).
The focus of this process was the separation of dichloroacetaldehyde (DCA) from chloral, rather than the separation of chloral from water. The azeotropic mixture, therefore, included EDC, chloral, water and DCA. Further, because of the focus of the process on DCA recovery, it was directed toward separation of components from an acetaldehyde chlorination mixture of 80% or more chloral and up to 12.5% water. No teaching is provided regarding application of the process to other feed streams or of the process parameters, i.e., the amount of EDC and temperature ranges necessary to achieve the reported results.
What is needed, therefore is a method for producing very dry chloral which meets at least the following criteria:
1. An azeotropic mixture should be used which readily allows separation of water from the chloral without use of extreme operating conditions, i.e., elevated pressures or temperatures. Also, the chloral must be easily separable from the azeotropic agent and other components in the mixture without compromising the dehydration process. To this end, the azeotropic mixture will preferably be binary, i.e., it will be formed principally of the dehydrating agent and water. PA0 2. Further, with respect to the first criteria, the dehydrating agent used in the process should be susceptible to separation from the anhydrous chloral product without significant contamination thereof. PA0 3. The process should be tolerant of feed stream composition changes. In particular, the process should be effective in producing very dry chloral even from feed streams containing as much as 40% water by weight. PA0 4. The process should also be effective with the use of a relatively broad range of chloral to dehydrating agent ratios (weight to weight). PA0 5. The process should also provide a method for production of chloral having a water content of 0.1% by weight or less. PA0 6. The process should also provide a relatively simple, cost-effective means of converting the aqueous waste streams from the manufacture of vinyl chloride, ethylene dichloride or, in general, the oxychlorination of ethylene, into a commercially viable product; e.g., technical chloral which can also be convened into other chloral-containing chemicals.
The present invention meets these above criteria, providing an improved process for preparation of anhydrous chloral.